Is the domain properly pointed to the server via your nameservers at your domain name registrar, and have you given them time to propagate? I wouldn't bother trying to work on a Joomla installation until you've got the domain working properly. You might place an index.html on the account for now until you're sure the domain has been setup properly.

As for the errors, you should upload a favicon for your website, and you should also have error pages for your users to land on when they hit a bad link. More on error pages here in the docs:Error Pages - cPanel Documentation